1. Field of Invention
The present invention relates to an apparatus and method for gain adjustment for analog YPbPr signals, and more particularly, to an apparatus and method for gain adjustment for analog YPbPr signals for high definition television (HDTV).
2. Description of Related Art
The front end system of the HDTV generally utilizes an analog-to-digital converter (ADC) to convert analog YPbPr input signals. The analog YPbPr input signal is often attenuated or amplified due to environmental factors, so the digitalized signal cannot extend to the maximum output range of the ADC, or exceeds it and becomes saturated. As a result, the contrast of the displayed frames is adversely affected. For example, under the circumstance that the maximum output range of the ADC is 00h-7Fh, the analog YPbPR input signal might only be converted to the range of 00h-5Fh due to attenuation, thus the frames are relatively dim. Alternatively, due to amplification, the analog signal might only be converted to the range of 00h-9Fh, thus resulting in output saturation.
In order to solve this problem, after the outputting of the ADC, a digital signal process is carried out in the conventional method, and then the digitalized YPbPr signal is adjusted, so that the digitalized YPbPr signal can cover the whole output range of the ADC. However, the conventional digital signal processing has many disadvantages.
As for the conventional method, data must be collected and histograms must be made, so as to determine the distribution of the digital signal. Since the process is relatively long and complicated, it is time consuming and imposes heavy burden on the system. In order to balance the quality and the cost, bandwidth and resolution are inevitably compromised. In addition, the signal range is non-linearly scaled in the conventional method, such that the image quality is negatively affected.